The horn keeps going off even after the car is off

Sticking contacts in the horn pad switch, bad clockspring and even a bad horn relay that is stuck or burned.

the horn that is going off will be energised by the alarm system. You need a shop that can fix car alarms not horns.

You can pull the fuse, disconnect the horn relay, or unplug the horn itself.

Need to put key in drivers door and lock and unlock. This should stop the horn immediatly and car should start.

There are 2 possibilities for this to happen. 1. Inside the steering column there is a faulty circuit. 2. The horn relay has an internal fault. The horn works on a grounding type system, which means that +12V is always available to the circuit and when grounding happens at any point it will activate the relay to send the voltage to the horns. So if your horn is randomly going off then there is a temporary grounding action somewhere.

If you stop the horn then your car is no longer road worthy. You have a short circuit, most probably by the steering wheel itself where the wire to the horn connects the horn button. Remove steering wheel and inspect contact strip first.

a new horn!

My horn is all set now. I took the steering wheel pad off and put electrical tape around the wires and put it back together. It has been fine sense. Thank God.

Common 1999 911 problem Stephanie that needs to be repaired by a qualified Porsche mech. He will need to remove face of your steering wheel and replace horn switch that has worn out and is loose inside steering wheel. Will only get worse and could cause you issues when you hit your brakes behind car(s) stopped for red light. Trust me - I almost got in a couple of fights as they thought I was being a wise guy & "playing Porsche games".
Lew Andersen

Normally there is a horn relay, try replacing that. The contacts can weld together and keep the horn on. If you take the relay out and leave it out, you won't have a horn but at least it won't be blowing all the time.